Lead compound catalyzed siloxane resin system

ABSTRACT

A molding compound contains an uncured siloxane resin, a lead containing catalyst, and a silane or polysiloxane containing an appreciable amount of silanol or alkoxy groups. The molding compound is relatively stable at flow temperatures but cures rapidly at molding temperatures. The molding compound is used in the transfer molding of transistor housings.

United States Patent Alekna [451 May 30,1972

[ LEAD COMPOUND CATALYZED [56] References Cited SILOXANE RESIN SYSTEMUNITED STATES PATENTS t k S ti .Y. [72] J Ale N 2,516,047 7 1950 DeCoste ..260/465 [73] Assignee: General Electric Company 2,855,378 10/1958 .260/46.5 3,208,961 9/1965 ....260/46.5 [22] Filed: Jan. 21, 19713,264,260 8/1966 Muller et a1. ..260/46.5

21 A 1. N 108 652 1 pp 0 Primary ExaminerSamuel l-l. Blech Related U.S.Application Data Atlvmey-E Philip Koltos [63] Continuation of Ser. No.782,470, Dec. 9, 1968, aban- [57] ABSTRACT one A molding compoundcontains an uncured siloxane resin, 21 [52] U 8 Cl 260/825 252/428252/430 lead containing catalyst, and a silane or polysiloxanecontaining an appreciable amount of silanol or alkoxy groups. The 260/18260/29'1 260/37 260/465 molding compound is relatively stable at flowtemperatures 260/465 E but cures rapidly at molding temperatures. Themolding com- "ll 47/04 Cosg 47/ gag/ 8 55 pound is used in the transfermolding of transistor housings. le 0 arc 6 Claims, No Drawings LEADCOMPOUND CATALYZED SILOXANE RESIN SYSTEM This application is acontinuation of application Ser. No. 782,470, filed Dec. 9, l968, nowabandoned.

This invention relates to improved catalyzed silicone resin moldingcompounds.

In preparing silicone resin molding compounds, one needs to blendsilicone resin, catalyst, and, ifdesired, filler. Since silicone resinsare generally hard and brittle at room temperature, it is necessary toheat the resin while the filler and catalyst are being mixed therewithin order to soften the resin sufficiently to permit uniform blending. Aproblem, however, arises in that heating the resin in the presence ofthe curing catalyst during mixing causes the resin to cure, as theseresin systems are therrnosetting. When such a heated catalyzed resinsystem is used in a transfer molding operation, the hot fluid catalyzedresin must be fluid enough to pass through the small transfer moldingchannel to the mold without setting in the channel, through the moldcavity without setting before the cavity is completely filled, and thencured shortly thereafter in order that the molding process be rapid.

The main object of the invention is to create a new silicone resincatalyst system which permits a silicone resin molding compound to beheated until it is fluid without danger of curing, but provides a fastcure of the resin system at a temperature slightly above the flowtemperature of the resin but below a temperature which would degrade thephysical properties of the cured resin.

The catalyst system which is used in the present invention iscatalytically active at high temperature but is relatively inactive atlow temperature. Apparently, what happens is that the catalyst employedcomplexes with silanol groups of the resin or with an added silanolcontaining silicone at higher temperatures and the complex formed issoluble in the resin. The soluble complex is active at high temperaturesbut is non-existent at low temperatures and the uncomplexed physicaladmixture is relatively inactive.

The thermosetting silicone resin molding compounds of this inventioncomprise an intimate mixture of (a) an uncured silicone resin containingat least 0.25 percent by weight of silicon-bonded hydroxyl groups orlower alkoxy groups having one to eight carbon atoms per group, and acatalytic amount of (b) a composition consisting of from one-half topercent and preferably from 1 to 4 percent by weight based upon thetotal weight of (a) (b) of a silane or siloxane containing silanolgroups or alkoxy groups, and from 0.01 to 5 percent by weight of acompound selected from the group consisting of 2PbCO PbCO Pb O Pb O andPbO When the siloxane resins contain more than 4 percent by weight ofsilicon-bonded hydroxyl groups, the silane or siloxane containingsilanol or alkoxy groups is no longer required, but is still preferred.It is preferred for ingredient (b) to contain from 1 to 4 percent of thesilane or siloxane compound and from 0.1 to 0.6 percent of the leadcompound. Any silane or low molecular weight polysiloxane fluidcontaining alkoxy or silanol groups is a suitable ingredient forcomponent (b).

Generally speaking, silanes which can be employed as an ingredient forcomponent (b) in the practice of the present invention are those fallingwithin the scope of the formula R,(OH),,(OR),.Si where R is selectedfrom the class comprising lower alkyl radicals having one to eightcarbon atoms; cycloalkyl radicals having five to seven carbon atoms inthe ring; lower alkenyl radicals having two to eight carbon atoms;mononuclear aryl radicals; mononuclear aryl lower alkyl radicals havingone to six carbon atoms in the alkyl group; and halogenated derivativesof the above radicals; OR is a lower alkoxy radical containing from oneto eight carbon atoms per radical; I has a value of l to 3; 14 has avalue ofO to 3; v has a value ofO to 3; and the sum ofu+ v has a valueof l to 3.

Generally speaking, siloxane compounds which can be employed as aningredient for component (b) in the practice of the present inventionare those falling within the scope of the formula R ,(HO),,(OR) ,SiOwhere R and (OR) are defined as R and (OR) respectively are definedabove; x

| II0sio Llml The choice of which silicon containing materials to use iningredient (b) depends in part on the length of storage, i.e., a morevolatile material will be lost to a greater degree on storage than aless volatile material, on the degree of plasticity desired in the finalcast resin, and the silanol content of the casting resin, i.e., if thesilanol content of the resin is relatively high, the silanol or alkoxycontent of the polysiloxane of component (b) can be relatively low, andin fact if the silanol content of the casting resin is over 4 percent byweight, the silanol containing polysiloxane of component (b) is notrequired as part of the catalyst system. It is preferred, however, touse a silanol containing polysiloxane fluid in combination with castingresins having a silanol content of over 4 percent as they act asplasticizers.

The siloxane resins that can be used in the composition of thisinvention are well known materials. By the term siloxane resin, is itmeant polymers containing two or more siloxane units, and having theaverage unit formula where R is selected from the same class as R; (OR)is selected from the same class as (OR); r has a value of 1.0 to 1.7 andpreferably has a value of 1.05 to 1.45; q has a value of O to 1.0 andpreferably a value of 0.2 to 0.55; r has a value ofO to 1.0 andpreferably has a value of 0.2 to 0.55 and the sum of q r has a value of0.01 to 1.0 and preferably has a value of 0.2 to 0.5 5.

Examples of siloxane units that can be present in the siloxane resinsare s s alzv e ah Q S SHH 02 3) B 5 r 2 5 3I 2, 2 5)2 (qrmq t a 1 a/z, a02 More specifically, R, R and R are selected from the class consistingof lower alkyl radicals, e.g., methyl, ethyl, propyl, butyl, and octylradicals; cycloalkyl radicals having five to seven carbon atoms in thering, e.g., cyclopentyl, cyclohexyl, and cycloheptyl radicals; loweralkenyl radicals, e.g., vinyl and allyl radicals; mononuclear aryl,e.g., phenyl, tolyl and xylyl; mononuclear aryl lower alkyl radicals,e.g., benzyl and phenylethyl radicals; and halogenated derivatives ofthe above radicals, e.g., chloromethyl, beta-chloroethyl, chlorophenyl,dibromophenyl and trifluoromethylethyl radicals. Preferably, R, R and Rare selected from the class consisting of methyl, ethyl and phenyl.

The lower alkoxy radicals, OR,(OR) and (OR) are selected from the classconsisting of lower alkoxy radicals having one to eight carbon atoms,e.g., methoxy, ethoxy, propoxy and isopropoxy radicals and is preferablyselected from the class consisting of the above specifically namedradicals.

The ratio of the organic substituents to the silicon atoms in theabove-described siloxane resin must be in the range of 1.0:1 to 1.711.Preferably, the resin has a phenyl to silicon ratio of 0.5: 1 to 0.7: land other substituents to silicon ratio of 0.5 :1 to 0.121, and atom]phenyl and other substituents to silicon ratio of 1.05:1 to 1.45:1. Thepreferred resins of this invention are the phenylmethylsiloxane resins,i.e., resins containing siloxane units containing phenyl groups, andsiloxane units containing methyl groups. The preferred resin containssome siloxane units having two monovalent hydrocarbon substituents persiloxane unit as this adds flexibility to the cured resin. Preferably,from 5 to 45 percent of the siloxane units contain two monovalenthydrocarbon substituents per siloxane unit.

In addition, the resin must contain at least 0.25 percent by weight ofsilicon-bonded OH and/or (OR) groups. The resin can contain a muchhigher percentage of OH groups and preferably contains at least 5 weightpercent of OH groups. At least 4 weight percent of OH groups and (OR)groups is a critical requirement if the lead containing catalyst is tobe used in the absence of the aforedescribed silane or siloxane fluid ofcomponent (b). It is preferable that 90 percent of the total OH and (OR)groups be OH groups. The (OR) groups are lower alkoxy groups having upto eight carbon atoms, such as methoxy, ethoxy and isopropoxy groups.The presence of such groups on methylsiloxy groups in the resin aids inregulating the cure time of the resin. As the ratio of alkoxy groups tosiloxy groups increases the cure time increases.

If desired, fillers and pigments can be added to the uncured resin toincrease the strength of the cured resin, reduce crazing, make a moreattractive product, etc. The particular pigment or filler employed inthe composition of this invention is not critical but fillers which havea catalytic effect in themselves toward the resin of this inventionshould be avoided. Alkaline fillers in large quantities and stronglyacidic fillers should be particularly avoided as should other fillerswhich exert a catalytic effect on the condensation of the siliconeresin. Some inert fillers which are suitable are ground glass,diatomaceous earth, crushed quartz, fume silica, precipitated silica,magnesium silicate, zirconium silicate, and aluminum silicate. Thepreferred filler are zirconium silicate, chopped glass fibers, aluminumoxide and fused silica. The amount of filler present in the resin canvary from percent up to the point where the filler concentration is sohigh that it interferes with the flow properties of the molding resin.This point is, of course, a function of the type of resin, the type andamount of plasticizer present, and the porosity of the filler.

Silicone resins which may be used in the practice of the presentinvention, generally speaking, are well known in the art. For example,see US. Pat. No. 2,646,441 of Duane, US. Pat. No. 3,135,713 of Brewer etal., and US. Pat. No. 3,3 89,1 14 of Burzynski et al. and the discussiontherein.

The preferred resins for use in the practice of the present inventionare those having a silanol (measured as OH) content of 5 to 7 percent byweight. The method of making such resins is generally set forth in US.Pat. application, Ser. No. 671,574 of Duane F. Merrill, filed Sept. 29,1967, now abandoned, entitled Silanol-Containing OrganopolysiloxaneResins and a Method for Making Them. In addition, the preferred resinsalso contain some siloxy groups which are substituted with one methylradical per siloxy unit and these mono-substituted siloxy units alsocontain some alkoxy substitution. It is the siloxy units in the resinwhich are mono-substituted with methyl groups and which also containsome alkoxy substitution which regulate the cure time of the resin. Ifthe resin contains over 5 percent silanol by weight and contains noalkoxy groups, the cure time of the resin at high temperatures can be sofast that it would be impractical to use such resin in transfer orinjection molding operations.

Silanol-containing organopolysiloxane resins having a silanol content of5 percent to l l or 12 percent can be made by hydrolyzingorganohalosilanes utilizing a water immiscible organic solvent andacetone as a cosolvent. The method involves agitating a mixturecomprising (A) organohalosilane preferably in combination with a loweralkyltrialkoxysilane, (B) water, (C) acetone, (D) a water immiscibleorganic solvent, and (E) an aliphatic monohydric alcohol having from oneto eight carbon atoms where there is present by weight in said mixture,per part by weight of A),

1.7 to 10 parts of(B),

0.2 to 5 parts of(C), and

0.3 to 5 parts of (D), and from 0 to 1 mole of (E) per mole of halogenattached to silicon of (A), (2) separating an organic solvent solutionof (F) from the resulting hydrolysis mixture of l where (F) is asilanol-containing organopolysiloxane having an average ratio of fromabout 1 to 1.8 organo radicals per silicon atom, and (A) is selectedfrom,

a. organotrihalosilane,

b. a mixture of ganodihalosilane,

c. the reaction product of (E) and a member selected from (a) and (b),which has an average ratio of up to 1 alkoxy radical per halogenradical,

d. a mixture of (c) and a member selected from (a) or (b), and where theorgano radicals of (A) and (F) are attached to silicon by carbon-siliconlinkages and are selected from monovalent hydrocarbon radicals,halogenated monovalent hydrocarbon radicals, and cyanoalkyl radicals.

Included by the organohalosilanes which can be employed in the practiceof the invention, are silanes of the formula,

L -i-G (I) where R is selected from the same class as R, X is a halogenradical, such as chloro, and a is an integer having a value of l or 2.In addition, there can be employed in combination withorganotrihalosilane and diorsuch organohalosilanes of formula l analiphatic monohydric alcohol of the formula,

ROH or an alkoxylated organosilane of the formula,

( )a( )b -1ab a where R is selected from the same class as R; X and aare as defined above; b is an integer equal to l to 3, inclusive; andthe sum of a and b is equal to 2 to 4, inclusive.

Included by the organohalosilanes of formula 1 are for example,methyltrichlorosilane, dimethyldichlorosilane,methylphenyldichlorosilane, phenyltn'chlorosilane,diphenyldichlorosilane, etc. Included by the partially alkoxylatedorganohalosilanes of formula (3), are reaction products oforganohalosilanes of formula (1), where R is preferably selected fromthe class consisting of monovalent hydrocarbon radicals and halogenatedmonovalent hydrocarbon radicals, with alcohols of formula (2) such asmethyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butylalcohol, etc.

In instances where the aliphatic monohydric alcohol of formula (2) isutilized in the practice of the invention, the alcohol can be addeddirectly to the organohalosilane of formula (1) before hydrolysis, or itcan be added to the hydrolysis mixture prior to the addition of theorganosilane. As a result, the silanol-containing organopolysiloxane ofthe present invention, can be free of, or contain chemically combinedalkoxy radicals attached to silicon.

The preferred uncured silicone resins of the present invention can havefrom 4 to 1 1 percent and preferably from 5 to 7 percent by weight ofhydroxy radicals attached to silicon. These resins are friable fastcuring molding materials when at percent solids. Experience has shownthat in most instances, the average ratio of the R radicals to siliconwill determine the nature of the resin and its utility. For example,resins at 100 percent solids, having an average ratio of about 1 toabout 1.2 R radicals per silicon atom, a silanol content of from 4 to 11percent by weight, with or without chemically combined alkoxy radicals,are generally friable, and suitable for molding applications. Thesemoldable materials have been found to soften at temperatures as low as60 C, and generally flow at temperatures between 70-90 C.

In accordance with the method of the invention, hydrolysis is achievedby agitating the organohalosilane in the presence of water, acetone, andorganic solvent. The organic layer is separated from the acid layerwhich forms during hydrolysis. The organic phase then is stripped toproduce a 100 percent solids resin.

Although the order of addition of the various ingredients is notcritical, it is preferred to add the organohalosilane to the mixture ofwater, acetone, and organic solvent. Preferably, a proportion of from 2to 6 parts of water, 0.3 to 2 parts of acetone, and 0.6 to 2 parts oforganic solvent, per part of organohalosilane can be employed. Suitableorganic solvents are for example, any water immiscible organic solventwhich is inert to the hydrolysis reactants during hydrolysis, and inwhich thehydrolyzate is soluble, to provide for its separation from theaqueous layer. For example, there can be employed a hydrocarbon such asbenzene, toluene, xylene, etc., esters such as butyl acetate and ethylacetate; ethers such as diethyl ether,dioxane, etc. During the addition,the mixture is agitated to provide for a sufficient degree of hydrolysisof the organohalosilane and formation of the organopolysiloxanehydrolyzate. The temperature of the hydrolysis mixture can be controlledby the rate of addition, or external heat or cooling can be employed ifdesired. During hydrolysis,a temperature between 0 to 80 C has beenfound effective, while a temperature between 20 to 40 C is preferred.After the addition has been completed, the mixture can be stirred for anadditional period of time, such as 30 minutes or more to allow forcomplete hydrolysis of the organohalosilanes. The mixture is thenallowed to settle and the acid layer can be drawn off from the organiclayer. The organic layer can then be stripped of solvent to 100 percentsolids.

When making molding resins, it has been found expedient to strip underreduced pressure, such as a pressure between 25 mm to 500 mm Hg. to asolids concentration of from 50 to 70 percent by weight of the resinsolution. Resin impurities can be removed at this solids concentration,such as by filtration, centrifuging, etc. Further stripping can beemployed to 100 percent solids at a temperature sufficient to remove allof the residual solvent. For example, when stripping toluene, atemperature up to 130 C has been found effective.

In instances where the average R to Si ratio is above 1.2, for example,1.2 to 1.4 or 1.4 to 1.8, it is preferred to strip at atmosphericpressure to a solids concentration of up to about 95 percent. If it isdesired, the resin can be refluxed 2 to 3 hours at temperatures between190 to 230 C, to further improve the characteristics of the resin.

The procedure generally followed in making the molding compounds of thepresent invention generally involves the following steps:

1. The materials which are to be added to the resin are blendedtogether, e.g., fillers such as glass fibers mixed with silica fillerand a release agent such as calcium stearate, along with color pigmentsand a catalyst such as lead carbonate in a high speed blade mixer at aspeed on the order of 4,000 rpm for approximately 4 minutes. After theingredients are thoroughly mixed, the silicone resin is added to themixer and is mixed in with the other components at a speed of about2,000 rpm for approximately 2 minutes. The molding compound is then madeby transferring the blend from the mixer into a double screw conveyorwhich feeds a rotor mixer. A temperature on the order of 80 to 100 C isemployed and a .rotor speed in the neighborhood of 500 t 100 rpm isemployed.

2. A catalyst complexing agent such as a silanol end-stoppedpolysiloxane containing both dimethylsiloxy and 'diphenylsiloxy units isthen pumped into the mixture in the rotor chamber. The output of therotor mixer which has been fluidized by the heat generated in the mixeris fed between two rollers where it is formed into a solid sheet. Thesheet is cooled to room temperature and granulated in a grinder to aparticle size of approximately 10 mesh. This 10 mesh particle sizemolding compound can be used, as is in an injection, transfer orcompression molding apparatus or can be pelletized before use in suchmolding apparatus.

The following examples are illustrative of the practice of my invention.

EXAMPLE 1 This example describes the manufacture of a molding resin andthe use of the molding resin in a transfer molding operation to make atransistor housing.

A silane blend composed of 19.5 moles of methyltriethoxysilane, 28.5moles of methyltrichlorosilane, 47 moles of phenyltrichlorosilane, and 5moles of dimethyldichlorosilane was hydrolyzed in a mixture of toluene,acetone and water. For every thousand parts of the silane blend, therewas 4,547 parts of the toluene-acetone-water mixture. The mixture wascomposed of 825 parts of toluene, 722 parts of acetone and 3,000 partsof water.

The hydrolysis was carried out by adding the silane blend to a preheatedmixture of the toluene, acetone and water. The silane blend was addedover a 25-minute period, during which time the temperature of thehydrolysis mixture went from 25 to 70 C. After the silane addition hadbeen completed, the hydrolyzate was agitated for 5 minutes. Theagitation was stopped and layers separated very rapidly. As soon as theseparation was completed, the resin was transferred into a bodyingkettle and vacuum stripped at 40 C to a solids content of 50 percent.

The resin which has been formed by the aforedescribed hydrolysis processwas then vacuum dried using a continuous film evaporator. When all ofthe solvent had been removed, the resin was then cast, cooled to roomtemperature, and ground to a fine powder. The resin should not beexposed to any appreciable amount of atmospheric moisture as it picks upwater which causes gassing when the resin is used in a moldingoperation. It is also necessary to perform the entire hydrolysis, dryingand grinding operation in equipment which does not add any catalyticmetal, especially iron, to the high silanol resin. In the presentexample, as much of the equipment as was possible was glass-lined.

A molding compound was made by adding to a high speed blade mixer, 17.3parts of chopped glass fibers, 17.3 parts of silica filler, 0.47 part ofcalcium stearate, and 0.7 part of lead carbonate. The components aremixed in a high speed blade mixer at a blade speed of 40,000 rpm for 4minutes. After the ingredients are thoroughly mixed, 15.4 parts of theabovedescribed resin is added to the mixture and is mixed in with theother components at a speed of 20,000 rpm for 2 minutes. The blend whichis formed is then transferred from the mixture into a double screwconveyor which feeds a rotor mixer. A screw chamber temperature of C anda rotor speed of 500 rpm is applied. Into the mixture in the rotorchamber is then pumped 0.67 part of a fluid of the formula (the dimethyland the diphenylsiloxy units are in random rather than blockarrangement). The output of the rotor mixer which had been fluidized bythe heat generated in the mixer was then fed between two rollers whereit was formed into a solid sheet. The sheet was cooled to roomtemperature and granulated in a grinder to a particle size ofapproximately 10 mesh. The molding compound which was formed by theabove method was then used in a transfer molding apparatus to formtransistor bodies. This involved heating the molding compound to 150 C,transferring the molten molding compound through the channels of amolding apparatus and into a mold cavity which had been heated to 175 C.The resin was allowed to cure in the mold cavity for 2 minutes. Thetransistor casing which had been formed was then removed and found to beperfectly formed having no voids or blow holes. The transistor was thenbaked for 2 hours at 200 C to eliminate any traces of moisture or gaseswhich had been formed during the molding operation. The transistor wasthen used in an electronic circuit and found to have excellentelectrical properties.

EXAMPLE 2 Following the method generally described in U.S. Pat. No.3,389,] 14 of Burzynski, a methylpolysiloxane resin was prepared. Theresin had a methyl to silicon ratio of one methyl radical per siliconatom, 6 percent by weight of silicon-bonded alkoxy groups, and 1 percentby weight of silicon-bonded hydroxyl groups.

Into a high speed blade mixer was added 40 parts of the resin, 60 partsof one-eighth inch Owens Corning hammer milled Fiberglas, 60 parts of325 mesh fused silica, l part of calcium stearate, 0.2 parts of leadcarbonate and 1 part of diphenylsilanediol. All of the above ingredientswere blended together in the high speed blade mixer until the mixturewas homogeneous. The composition was then milled on a two-roll mill at atemperature of l C for minutes, the resulting composition was cooled to25 C and granulated. The composition was then molded for 3 minutes at175 C and 1,000 psi to produce a 6 X 6 X l l 6 inch test specimen. Themolded sample, when removed from the hot mold was rigid, unblistered andfree of any voids. The sample had the following properties:'

Flexural Strength (ASTM D790) 9200 psi Tensile Strength (ASTM E638) 4600psi Dissipation Factor [0 Hz (ASTM Dl50) As Received 0.00l After 24hours in water at 25 C. 0.002

Example 2 was repeated except that the 1 part of diphenylsilanediol wasreplaced with 1 part of resorcinol. The test specimens produced werevery badly blistered and had many voids. The test specimens produced hadthe following properties:

Flexural Strength 5200 psi Tensile Strength 2100 psi Dissipation FactorAs received 0.00]

After 24 hours in water at 25 C. 0.01

The molding compound produced using the diphenylsilanediol was used intransfer molding of transistor housings. This involved casting a housingaround a transistor junction resulting in the embedding of thetransistor junction within the housing. After molding, the transistorhousings were subjected to a heat treatment of 200 C for 2 hours tocompletely remove any entrapped alcohol, water or gases. The transistorsproduced were of uniform quality and had excellent electricalproperties.

EXAMPLE 3 According to the general method described in Merrill patentapplication, Ser. No. 671,574, filed Sept. 29, 1967, now abandoned, aphenylpolysiloxane resin was prepared. The resin contained 7.0 percentby weight of silicon-bonded hydroxyl groups, and had a ratio of phenylradicals to silicon atoms of 1.0.

A molding compound was formulated by first mixing 40 parts of the resin,60 parts of one-eighth inch Owens Corning hammer milled Fiberglas, 60parts of 325 mesh fused silica, 1 part of calcium stearate, 0.2 part oflead carbonate, and 1 part of diphenylsilanediol. All of the aboveingredients were blended together in a high speed blade mixer and thenmilled on a two-roll mill at a temperature of C for 5 minutes. Theresulting composition was cooled to 25 C and granulated. The moldingcompound produced was then molded for 3 minutes at 175 C at 800 psi toproduce a 6 X 6 X l/l6 inch test specimen. The test specimen was rigid,unblistered and free of voids, and had the following properties:

Flexural Strength 8900 psi Tensile Strength 4200 psi Dissipation FactorAs molded 0.00!

After 24 hours in water at 25 C. 0.002

The molding resin produced was then used in the transfer molding oftransistor housings. After molding, the transistor housings weresubjected to a heat treatment of 200 C for 2 hours to completely removeany entrapped alcohol, water or entrapped gases. The transistorsproduced were of excellent uniform quality.

Example 3 was repeated except that one part of hydroquinone wassubstituted for the one part of diphenylsilanediol. The test specimensproduced were very badly blistered and had many voids, The testspecimens had the following properties:

Flexural Strength 4200 psi Tensile Strength 1800 psi Dissipation Factor1 As produced 0.00l

After 24 hours in water at 25 C. 0.021

EXAMPLE 4 By the method described in U.S. Pat. application, Ser. No.671,574 of Merrill, now abandoned, a resin was produced which containedon a molar basis 50 percent methylpolysiloxane units and 50 percentphenylpolysiloxane units. The resin was solid and contained 5 percent byweight of silicon-bonded hydroxy groups and 2 percent by weight ofsilicon-bonded isopropoxy groups. The ratio of methyl groups to siliconatoms was 0.5 as was the ratio of phenyl groups to silicon atoms.

A mixture was formulated containing 40 parts of the resin, parts of 325mesh fused silica, 1 part of calcium stearate, 0.2 part of leadcarbonate, and 1 part of vinyltriethoxysilane. All of the aboveingredients were blended together in a high speed blade mixer and werethen milled on a two-roll mill at a temperature of 90 C for 5 minutes.The resulting molding compound was cooled to 25 C and granulated. Themolding compound was then heated in a die for 3 minutes at C and 800 psito produce a 6 X 6 X l/ l6 inch test specimen. The test specimenproduced was rigid, unblistered and free of voids. The test specimen hadthe following properties:

Flexural Strength 10,200 psi Tensile Strength 5,600 psi DissipationFactor Original 0.00l

After 24 hours in water at 25 C. 0.002

The molding compound was used to make transistor housings in a transfermolding apparatus. After molding, the transistor housings were subjectedto a heat treatment of 200 C for 2 hours to completely remove anyentrapped alcohol, water and entrapped gases. The transistors producedwere of uniformly good quality with excellent electrical properties.

The above-described example was repeated except that one part ofpropylene glycol was used to replace the vinyltriethoxysilane. The testspecimens produced were very soft which indicated poor cure, were verybadly blistered, and had the following physical properties:

Flexural Strength 4100 psi Tensile Strength 2400 psi Dissipation FactorOriginal 0.001

After 24 hours in water at 25 C. 0.024

EXAMPLE Into a hydrolyzer was charged 918 parts of isopropyl alcohol.Over a 2-hour period, 1,000 parts of methyltrichlorosilane was slowlyadded to the alcohol. The reaction temperature was maintained below 40 Cby external cooling until escaping l-lCl started to cool the reaction.The temperature of the reaction dropped to C toward the end of thesilane addition. After all of the methyltrichlorosilane had been added,hydrogen chloride was removed from the reaction mixture by theapplication of vacuum, gradually, as the temperature was slowlyincreased to 100 C. After the hydrogen chloride had been stripped fromthe partially alkoxylated silane, the partially alkoxylated silane wascooled to 25 C. The silane was 75 percent alkoxylated, that is to say,75 percent of the chlorine atoms in the silane were replaced byisopropoxy groups.

The partially alkoxylated silane was placed in a hydrolyzer, and 1,045parts of toluene was added. A mixture of 200 parts of acetone and 200parts of water was then added to the hydrolyzer over a 40-minuteinterval. The reaction temperature was controlled with external coolingto maximum temperature of 40 C. Immediately following the addition ofthe water-acetone mixture, 200 parts of additional hydrolysis water wasadded over a 5-minute period, cooling was discontinued and the productwas agitated for 25 minutes. To the hydrolyzate was added 866 parts ofwash water and the agitation was continued for minutes. The water wasthen allowed to settle for 30 minutes and was drawn off as the lowerlayer. The hydrolyzate was then vacuum stripped at a temperature below50 C to 70 percent solids. The hydrolyzate was then filtered throughFullers earth. The hydrolyzate was then heated to 80 C and a partialvacuum was applied. The temperature was slowly increased to 150 C over a30-minute period. The vacuum applied was also slowly increased over thisperiod. The temperature was then held at 150 C for 30 additional minutesuntil all of the solvent was removed by vacuum stripping. After thesolvent was stripped, a resin remained in the hydrolyzer in a moltenstage. The resin was cooled to room temperature and ground to a 30 meshparticle size.

A molding compound was prepared by mixing 1 12 parts of 325 mesh fusedsilica filler, 1 part of zinc stearate, 36 parts of the above-describedresin, 0.165 parts of PbO and 3 parts of diphenylsilanediol. The mixturewas milled at 80 C for 5 minutes in a high speed blade mixer. Themolding compound was tested for flow and moldability on a Hull transferpress. The flow at 175 C and 800 psi was 41.5 inches and the molded partafter a 3-minute cure cycle had no blisters or voids. The Rockwellhardness on the M scale was 75M indicating excellent cure. The moldingresin was also used in the fabrication of transistor housings and thetransistors produced were of uniform excellent quality.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A composition comprising (a) an uncured silicone resin containing atleast 0.25 percent by weight of silicon-bonded groups selected from theclass consisting of hydroxyl groups and lower alkoxy groups of theaverage unit formula,

)q( 0R3 )r s (4qrs)l 2 where R is selected from the class comprisinglower alkyl radicals having one to eight carbon atoms; cycloalkylradicals having five to seven carbon atoms in the ring; lower alkenylradicals having two to eight carbon atoms; mononuclear aryl radicals;mononuclear aryl lower alkyl radicals having one to six carbon atoms inthe alkyl group; and halogenated derivatives of the above radicals; (OR)is a lower alkoxy radical containin from one to eight carbon atoms perradical; q has a value of to 1.0; r has a value of0 to 1.0; s has avalue of 1.0

to 1.7; and the sum ofq+rhas a value of0.0l to 1.0 and (b) a catalystsystem comprising,

I. from 0.01 to 5 percent by weight based upon the total weight of (a)and (b) of a compound selected from the group consisting of2PbCO3'Pb(OH)g, PbCO Pb o Pb Q, and Pb0 and 2. from one-half to 10percent by weight based upon the total weight of (a) (b) of a compound,other than the resin, selected from the class consisting of i. a silaneof the formula,

where R is selected from the class consisting of lower alkyl radicalshaving one to eight carbon atoms; cycloalkyl radicals having five toseven carbon atoms in the ring; lower alkenyl radicals having two toeight carbon atoms; mononuclear aryl radicals; mononuclear aryl loweralkyl radicals having one to six carbon atoms in the alkyl group; andhalogenated derivatives of the above radicals; OR is a lower alkoxyradical containing from one to eight carbon atoms per radical; t has avalue of l to 3; u has avalue ofOto 3, v has a value of0 to 3; and thesumofu+ v hasavalue of l to 3;

ii. a siloxane compound having the average unit formula,

.r( z t4.ruz)l 2 where R and (OR) are defined as R and (OR),respectively are defined above; .x has a value of l to 3 and when x hasa value of less than 1.7, there are at least 5 percent by weight basedupon the weight of the siloxane compound of HO and (OR) groups in thesiloxane compound; y has a value of 0 to 2; 1 has a value of O to 2, andthe sum ofy 1 has a value of0.02 to 2,

and (c) a filler.

2. The composition of claim 1, wherein (b) contains lead carbonate.

3. The composition of claim 1, wherein q has a value of 0.2 to 0.55; rhas a value of0.2 to 0.55; and s has a value of 1.05 to 1.45.

4. The composition of claim 1, wherein the sum of q r has a value ofO.2to 0.55.

5. The composition of claim 1, wherein the resin contains from 4 to l 1percent of silicon-bonded groups selected from the class consisting ofhydroxyl groups and alkoxy groups.

6. The composition of claim 1, wherein the resin contains from 5 to 7percent by weight of groups selected from the class consisting ofhydroxy and lower alkoxy groups.

2. from one-half to 10 percent by weight based upon the total weight of(a) + (b) of a compound, other than the resin, selected from the classconsisting of i. a silane of the formula, Rt(OH)u(OR)vSi where R isselected from the class consisting of lower alkyl radicals having one toeight carbon atoms; cycloalkyl radicals having five to seven carbonatoms in the riNg; lower alkenyl radicals having two to eight carbonatoms; mononuclear aryl radicals; mononuclear aryl lower alkyl radicalshaving one to six carbon atoms in the alkyl group; and halogenatedderivatives of the above radicals; OR is a lower alkoxy radicalcontaining from one to eight carbon atoms per radical; t has a value of1 to 3; u has a value of 0 to 3, v has a value of 0 to 3; and the sum ofu + v has a value of 1 to 3; ii. a siloxane compound having the averageunit formula, R2x(HO)y(OR)2zSiO(4 x y z)/2 where R2 and (OR)2 aredefined as R and (OR), respectively are defined above; x has a value of1 to 3 and when x has a value of less than 1.7, there are at least 5percent by weight based upon the weight of the siloxane compound of HOand (OR)2 groups in the siloxane compound; y has a value of 0 to 2; zhas a value of 0 to 2, and the sum of y + z has a value of 0.02 to 2,and (c) a filler.
 2. The composition of claim 1, wherein (b) containslead carbonate.
 3. The composition of claim 1, wherein q has a value of0.2 to 0.55; r has a value of 0.2 to 0.55; and s has a value of 1.05 to1.45.
 4. The composition of claim 1, wherein the sum of q + r has avalue of 0.2 to 0.55.
 5. The composition of claim 1, wherein the resincontains from 4 to 11 percent of silicon-bonded groups selected from theclass consisting of hydroxyl groups and alkoxy groups.
 6. Thecomposition of claim 1, wherein the resin contains from 5 to 7 percentby weight of groups selected from the class consisting of hydroxy andlower alkoxy groups.